This invention relates to magnetic recording systems, and especially those of the type used principally with computer systems for data storage. The invention is particularly apt for improvements in controlling the spacing of a magnetic head flying above the surface of a magnetic medium, doing so simply according to the detected relative strengths of signals of varying frequency on the medium.
Workers in the art of magnetic recording are aware of recording equipment and techniques intended to improve the density and accuracy of recording and/or detecting of digital data; especially as applied to magnetic disk memory files as adapted for buffer data storage with computer equipment. Such files typically involve magnetic transducers "flown" a few u-in. (micro-inches) above the recording surface of a magnetic disk. The heads commonly used for this comprise a set of transducer cores whose recording faces are fashioned very carefully to a precise profile which is optimum for the aerodynamics involved.
More particularly, such heads are typically supported very closely adjacent the disk surface on a fluid film (air bearing) developed by the rapid relative translation of the disk surface. The air bearing is understood as formed by a thin film of air swept into the head/disk gap and developing sufficient pressure to maintain the head at a prescribed distance -- this being herewith known as head/disk spacing (d.sub.h). Typically, this separation d.sub.h is on the order of only several dozen microinches or less.
As workers are aware it is becoming more and more critical to maintain this intimate head spacing, especially as bit densities increase, as disk speeds increase, and as the recording films become thinner and thinner, with adequate signal strength becoming more and more critical. Of course, it is catastrophic for such a flying head to "crash" onto the passing disk; this must be prevented at all costs. It is equally important to assure that this head spacing hd (which is critical for predictable read/write functions) is precisely maintained -- since, for instance, a loss of signal strength resulting from hd variance may distort or lose magnetic information and compromise the entire memory system. The mechanical performance of such a flying head is a function of this head spacing, or flying height. Workers will recognize, in short, that head spacing is a most critical factor in assuring accurate recording and detection of magnetic information.
Moreover, head spacing systems are becoming relatively more sophisticated and it is becoming ever more important to control the rate and angle at which a head approaches a rotating disk surface (e.g., when the air bearing effect is first established) -- not only to prevent a "crash", but to accelerate head actuation and foreshorten access time. Conversely speed is equally important when retracting the head from a disk. Workers will recognize that any time lost in this operation amplifies "access time"; a factor which is becoming more and more critical. Some actuation systems are presently contemplated which control the "landing and take-off" of such a flying head in a manner quite similar to that exercised in flying aircraft. It is an object of this invention to provide improved control of head spacing with a system simply involving signals recorded on the media at two key frequencies and detected and combined so as to be optimized only at a proper nominal spacing.